1. Field of the Invention
The present invention relates to a positional information determining apparatus, and is preferably applied to a global positioning system (GPS) navigation system that receives satellite waves coming from a plurality of GPS satellites, for example.
2. Description of the Related Art
Global Positioning System (GPS) navigation systems are each comprised of a GPS receiver and a navigation device in combination. A GPS navigation system is designed such that a navigation device display on a map the current position of the GPS navigation system itself detected by a GPS receiver.
In practice, the GPS receiver is designed to obtain positional information by analyzing satellite waves received from a plurality of GPS satellites (for example, four pieces) via GPS antennas, calculate the current position of the GPS navigation system based on the positional information, and output the positional data denoting the current position to the navigation device.
The navigation device is designed to display a map showing the surroundings of the current position on a monitor such as a liquid crystal display based on the positional data denoting the current position as well as an icon in a given shape indicating the current position, thereby visually indicating the current position of a user on the map.
Some GPS receivers are wirelessly connected to navigation devices so as to output positional data denoting current positions to the navigation devices. (e.g. refer to Page 2 and FIG. 10 in Japanese Patent Application Laid-Open No. 2002-156438)
Because such GPS receivers as configured above are wirelessly connected to navigation devices, they require an enormous amount of transmit power to emit radio waves by constantly putting radio communication means into operation, compared to those constructed in a wired connection, causing an increase in overall power consumption.
In particular, detachable mobile GPS navigation systems have a problem that operating time is shortened in mobile use when the GPS receivers consume a considerably large amount of power.